1. Field of the Invention
This invention relates to a d-c uninterruptible power supply (UPS) and more particularly to circuitry which can be used in conjunction with a conventional d-c power supply in order that the combination of the conventional supply and the circuitry forms a d-c UPS.
2. Description of the Prior Art
D-C power supplies are often used to provide one or more substantially regulated d-c voltages of relatively low amplitude(s) to a load such as a microcomputer or microprocessor (mpu). The d-c voltages, derived typically from a-c line voltage, are used to provide power to the various circuits of the load such as the memory of the mpu. Many loads and in particular mpu's require that the d-c voltages be applied on a continuous and uninterruptible basis in order that the load operate properly. Even the momentary loss of d-c power to a load such as an mpu will deleteriously affect the operation thereof. For example, the memory devices of the mpu may store false information that was not there originally. Moreover, when power is restored, the microcomputer could receive erroneous command signals. Hence, it is most desirable that d-c power be constantly supplied to a load such as an mpu so that it will not adversely suffer from a loss of a-c line voltage.
For many loads of the type described above the d-c voltages are provided by a commercially available power supply of the type which has its inputs connected to receive the a-c line voltage. The supply then rectifies the line voltage to provide therefrom and store in a convenient energy storage device, such as a capacitor, a d-c voltage of relatively high amplitude. The supply then includes a power switch in the form of a d-c to d-c converter which converts this relatively high amplitude d-c voltage into the one or more relatively low amplitude d-c voltages to be supplied to the load. In many cases the power supply is designed in a manner such that the d-c to d-c converter receives all of the input signals necessary for its operation from the relatively high d-c voltage generated by the rectifier and not by reason of any separate connection of the converter to the a-c line voltage. It has been found that power supplies of that type may be easily and inexpensively converted into a d-c UPS to thereby provide the desirable uninterrupted d-c voltages to the load by the addition of the circuit of the present invention.